This invention relates to a synthetic resin molding for the use of automotive vehicles, particularly of the type in that a long molding product such as a side molding, a wind molding, a bumper molding, or the like is cut in a predetermined length for use.
As is shown in FIG. 4 a synthetic resin molding for the use of automotive vehicles such as a side molding 43 which is to be mounted on a body 41 of an automotive vehicle 40, a wind molding 45 which is to be mounted on a window frame of the vehicle 40 or a bumper molding 44 which is to be mounted on a bumper 42 of the vehicle 40, is of the type in that a long synthetic resin molding product, when to be mounted, is cut in a predetermined length, Therefore, when the mounted synthetic resin material is often contracted in the longitudinal direction due to change of exteral temperature, gaps are created at the end portions of such molding. This naturally badly spoils the outer appearance of such automotive vehicles and thus undesirable. In addition, a peeling-off is easily taken place due to deformation of the mounting or attaching surface of the molding. Therefore, each maker requests the coefficient of contraction to be within a predetermined range at a certain temperature in view of a difference in temperature between the severe cold time in winter and the severe hot time in summer.
To this end, an elongated molding product of a synthetic resin material has been annealed at a high temperature in order to stabilize the coefficient of contraction or a sheet of metal aggregate comprising a strip-shaped piece of iron, aluminium, stainless steel or the like has been subjected to insert-molding in order to restrict the coefficient of contraction.
However, in the conventional means for annealing an elongated molding product of a synthetic resin material, the annealing must be repeated until the coefficient of contraction of the molding product is brought to be within an allowable range. Therefore, the number of manufacturing steps is necessarily large and costs are increased due to comparatively long manufacturing time. Moreover, even by this, a completely satisfactory result is unobtainable.
On the other hand, one that is obtained by insert-molding of an aggregate of iron or the like is excellent in strength at the mounting portion, in automorphic ability, in small coefficient of contraction in the longitudinal direction of its entirety, etc. However, it has the shortcomings in that the cutting is not easy, that treatment of the end portions thereof are troublesome when the aggregate is an iron plate or the like because the end portions easily rust, and that the costs are increased in case the aggregate is aluminium or stainless steel.